Vertical rate (ft/min)
Name Minimum Maximum Strength (g) Available from
COC .∞ ∞ 0 All DES1500 .∞ .1500 1/4 COC CL1500 1500 ∞ 1/4 COC SDES1500 .∞ .1500 1/3 CL1500, SCL1500, SCL2500, SDES2500 SCL1500 1500 ∞ 1/3 DES1500, SDES1500, SDES2500, SCL2500 SDES2500 .∞ .2500 1/3 DES1500, SDES1500 SCL2500 2500 ∞ 1/3 CL1500, SCL1500
TCAS has the option to strengthen the original advisory or reverse the sense of the advisory. Once an advisory has been strengthened, TCAS may later weaken the advisory. All subsequent advisories are assumed to be responded to with a stronger 1/3 g maneuver.
The
set
of
advisories
used
in
this
report
for
the
DP
logic
is
summarized
in
Table
1.
In the table, COC stands for “clear of con.ict,” which means that no advisory has been issued or there is no longer a threat. The sense of the advisory is labeled either CL or DES, for either climb or descend, respectively. The pre.x “S” indicates that a stronger response is assumed. Only the minimum and maximum rates are typically displayed to the pilot, and not the “strength” of the response, so the six advisories in the table (not including COC) only correspond to four di.erent advisories to be displayed to the pilot. However, it is useful to distinguish the advisories according to the assumed strength of the maneuver when developing the MDP model.
Table
1
also
indicates
the
availability
of
each
advisory
given
the
current
advisory
on
display.
For example, COC can be issued at any time. However, because DES1500 and CL1500 are initial advisories, they can only be issued if COC is on display to the pilot. The advisory SDES1500 can be issued following CL1500, SCL1500, and SCL2500, in which case it acts as a reversal, or following SDES2500, in which case it acts as a weakening. Because SDES1500 is a subsequent advisory, it cannot be issued following COC. It also cannot be issued following DES1500 because they are fundamentally the same advisory, di.ering only in strength.
The
advisories
in
Table
1
are
a
subset
of
the
advisories
available
in
the
current
version
of
TCAS. Although it captures all of the “corrective” advisories issued by TCAS, it does not contain certain “preventive” advisories. TCAS can issue advisories such as “do not climb” to prevent an aircraft from climbing into another aircraft. These preventive advisories are less disruptive to the .ight path of the aircraft. However, there is currently some debate within the TCAS development community about the utility of such advisories. Although this report does not incorporate preven-tive advisories, it is straightforward to include them. The computational and storage requirements of the MDP approach scale linearly with the addition of new actions.
The collision avoidance system may choose to initially issue either DES1500 or CL1500. Following an initial 5s delay, the pilot of the own aircraft will respond with a 1/4 g maneuver, if necessary, to achieve the required vertical rate. Following the initial advisory, the system may choose to either terminate the advisory, strengthen the advisory, or reverse the advisory. If the advisory is strengthened, the pilot will maneuver at 1/3g after a 3s delay to achieve a vertical rate of 2500ft/min in the direction of the original advisory. If the advisory is reversed, the pilot will maneuver at 1/3g after a 3s delay to achieve a vertical rate of 1500ft/min in the opposite direction of
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